British scientists have analysed samples from the site of a suspected chemical attack in Syria and concluded that sarin or a sarin-like substance was used, the British ambassador to the United Nations said today.

'The United Kingdom therefore shares the US assessment that it is highly likely that the regime was responsible for a sarin attack on Khan Sheikhun on the 4th of April,' Ambassador Matthew Rycroft told the UN Security Council.

Turkish health officials on Tuesday said post-mortem tests on victims of the suspected attack had also concluded that the deadly sarin nerve agent had been used.

The results came from analysis of blood and urine samples of the casualties from the attack in Idlib province who were brought to Turkey for treatment. Three of them died in hospital.

At least 87 people including 31 children died in the suspected attack that the West blames on Syria President Bashar al-Assad's forces.

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British scientists have analysed samples from the site of a suspected chemical attack in Syria and concluded that sarin or a sarin-like substance was used, the British ambassador to the United Nations said today

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Assad's forces have been blamed for the attack, but Russian President Vladimir Putin, a key ally of the Syrian leader, has again angrily rejected the accusation today.

If Russia uses its veto, it will be the eighth time it has done so in favour of the Syrian regime.

The draft resolution is similar to a text circulated to the 15-member council last week that condemns the April 4 attack and pushes Syria's government to cooperate with investigators.

Russian deputy foreign minister Gennady Gatilov told Interfax news agency: 'In its current form this project is unacceptable for us. We, of course, will not vote for it.'

A Syrian child is treated in the aftermath of last week's attack in the Idlib province in northern Syria

Turkish health minister Recep Akdag said Assad should be tried as a war criminal after he announced that blood and urine tests on victims confirmed the presence of the lethal gas.

Akdag, in comments reported by the state-run Anadolu agency, said that international organizations and United Nations, 'should declare Assad as a war criminal and put him on trial'.

He said: 'It has been identified that sarin gas was used.'

The Syrian government has denied carrying out the attack, and Russia has defended its ally, denying that President al-Assad's regime had used chemical weapons.

The international chemical weapons watchdog has scheduled a meeting of its executive council to discuss the alleged use of chemical weapons in Syria

Putin today accused Assad's opponents of planning to stage chemical attacks to be blamed on Damascus in order to lure the United States deeper into the conflict.

The Kremlin leader again slammed the US missile strike and angrily rejected the allegation that Assad's forces were behind the suspected chemical attack on the town of Khan Sheikhun that left 87 civilians dead including children.

'Where is the proof that Syrian troops used chemical weapons? There isn't any. But there was a violation of international law. That is an obvious fact,' Putin told Mir television, in a statement released by the Kremlin.

The United Nations peace envoy for Syria today urged the US and Russia to agree on a way forward to end the war in Syria and pave the way for a 'real negotiation'.

Russian Foreign Minister Sergei Lavrov (right) and US Secretary of State Rex Tillerson (left) shake hands for the media during their meeting in the Russian Foreign Ministry guest house in Moscow today

Special envoy Staffan de Mistura told the UN Security Council that he was ready to convene a new round of talks in May but that US-Russian cooperation was needed.

His appeal came as US Secretary of State Rex Tillerson was in talks in Moscow with his Russian counterpart Sergei Lavrov following US missile strikes in Syria in retaliation for a suspected chemical attack.

The two countries have 'serious differences' but also a 'common interest' in ending the six-year war that has killed 320,000 people, De Mistura said.

'They must find a way to work together to stabilize the situation in a deliberate, realistic and concerted way in support of the political process,' he said.

He said the UN is ready to lead a 'real negotiation' on a 'package for an orderly, mapped-out, credible and irreversible, agreed political transition' to end the war.

Russia is expected to veto the measure - which would mark the eighth time that Moscow has used its veto power to block Security Council action directed at its ally, Syria.

'Let us view this moment of crisis - and it is a moment of crisis - as a watershed and an opportunity for a new level of seriousness in the search for a political solution,' said De Mistura.